The three olefins (i.e., “ethylene, propylene and butane”) and three aromatic hydrocarbons (i.e., “benzene, toluene, xylene”) are vital basic organic chemical materials, especially the production capability of ethylene is often regarded as a symbol of the development level of petrochemical industry in a country and region. Due to the explosive development of energy storage battery technologies and the imminent implementation of the “National VI” vehicle exhaust emission standards in the People's Republic of China (PRC), which is so-called the world's most stringent standards for vehicle exhaust emission, the electric vehicles have emerged as the rising alternative of the fuel oil vehicles by virtue of the advantages such as the near zero pollution during the driving process, energy saving, low cost of use and may be easily intelligentized, it has become an irreversible development trend that the fuel oil vehicles will be replaced by the electric vehicles, the subsequent result will be a sharp decline of the oil consumption in the transportation industry, thus it is urgent for the petroleum processing enterprises to transform its production mode from “fuel oil dominated pattern” to “chemical products dominated pattern”.
At present, about 95% of ethylene and 66% of propylene in the world are produced by a tube furnace steam pyrolysis process using light weight raw materials such as natural gas, naphtha or light diesel oil. However, in view of the gradual depletion of conventional crude oil resources since the 21st century, the crude oil supply in the world has presented the development trends of heavy weight and inferior quality, leading to a relative deficiency of light weight cracking raw materials, while the worldwide market demand for low-carbon olefins is growing rapidly. In order to alleviate the imbalance between the supply and demand, broaden the raw materials for producing the low-carbon olefins, and make better use of heavy feedstock oil, the development of “chemical products dominated pattern” technical routes that use heavy oil as a raw material to directly produce low-carbon olefins through catalytic cracking process has become the focus and hotspot of research in the petroleum refining industry at home and abroad, however, there are very few mature technologies that can be industrialized.
Many technologies of catalytic cracking heavy oil for producing low-carbon olefins have been developed in recent years, and have attracted the widespread interest and demonstration applications in the industry, for example, the DCC/CPP process developed by the Sinopec Research Institute of Petroleum Processing; the PetroFCC process developed by the Universal Oil Products (UOP) Company in the Unites States of America (USA); the High Severity Fluidized Catalytic Cracking (HS-FCC) process and the THR technology developed by the Japan Petroleum Energy Center (JPEC); the TCSC process developed by the German Institute of Organic Chemistry; the INDMAX (UCC) process developed by the Indian Oil Corporation (IOC), the Maxofin process jointly developed by the Exxon Mobil and the Kellog, and the two-stage riser catalytic cracking (TMP) process proposed by China University of Petroleum (CUP). Compared with steam cracking process, the technologies of catalytic cracking heavy oil for producing low-carbon olefins have the advantages such as widened feedstock ranges of olefins, low reaction temperature, easy adjustment of the product distribution, and low energy consumption. On the one hand, these catalytic cracking processes should adopt the operation modes with high temperature, short residence time, large catalyst/oil ratio and water/oil ratio. On the other hand, both the composition of raw materials and the properties of catalyst are key factors affecting the yield and distribution of the catalytic cracking products during the catalytic cracking operation process. However, the active components of the shape selective catalyst for heavy oil catalytic cracking are mainly ZSM-5 and Y-type molecular sieves, whose pore structures have a small size, so the diffusion of large heavy oil molecules are limited during the mass transfer process, and it is difficult for the large heavy oil molecules to enter into the molecular sieves to conduct a shape-selective cracking; moreover, the acidic molecular sieves have a strong hydrogen transfer performance, which leads to a limited increase in the yield and selectivity of the olefins. In addition, the heavy oil macromolecules accumulated on the surface of molecular sieves are prone to overcracking under the action of the acid site, resulting in poor product distribution or coking and condensation, thereby blocking the pore channels of catalyst. At present, the existing industrial shape selective catalysts are used to prepare low-carbon olefins through catalytic cracking of the inferior materials such as atmospheric pressure residue oil, vacuum residue oil, deasphalted oil, which often leads to many problems such as catalyst poisoning, poor atomization effect, large amount of generated coke, and significantly lowered conversion rate and selectivity.
In addition, during the existing process of petroleum thermal processing, the hydrocarbon reaction mainly occurs in the form of liquid phase reaction. In the gaseous phase, hydrocarbon molecules can be quickly dispersed after being split into free radicals, while the free radicals in the liquid phase are surrounded by neighboring molecules which resemble a “cage”, and the condensation polymerization will be intensified. In order to disperse the formed free radicals, it is necessary to overcome the additional potential barrier so as to diffuse out of the “cage”, which is the so-called “cage effect”. Such a “cage effect” may alter the activation energy and reaction rate of the liquid phase reaction relative to the gaseous phase reaction.
The process of directly preparing basic chemical raw materials from crude oil will significantly shorten the petroleum refining process, eliminate the processes such as atmospheric and vacuum distillation and coking, and will greatly reducing the energy consumption of processing. However, how to eliminate the pollution of residual carbon and heavy metal in the crude oil and maximize the acquired amount of three olefins and three aromatic hydrocarbons have emerged as a major issue which shall be urgently resolved in the transformation and upgrading process of processing petroleum with “chemical products dominated pattern” in the world.